Light from a laser forms a 1.31-mm diameter spot on a wall. If the light intensity in the spot is $1.58 \times 10^4 \mathrm {~W} / \mathrm { m } ^ { 2 }$ what is the power output of the laser? Assume that all the light emitted by the laser hits the spot.
A) 21.3 mW
B) 13.2 mW
C) 17.9 mW
D) 24.7 mW

Question

Quizplus · Accepted Answer

The power output of the laser is equal to the intensity of the light in the spot multiplied by the area of the spot. The area of the spot is given by:$$A = \pi r^2 = \pi (0.655 	imes 10^{-3} \mathrm{~m})^2 = 1.34 	imes 10^{-6} \mathrm{~m}^2$$Therefore, the power output of the laser is:$$P = IA = (1.58 	imes 10^4 \mathrm{~W/m^2})(1.34 	imes 10^{-6} \mathrm{~m}^2) = 21.3 \mathrm{~mW}$$

Light from a Laser Forms a 1 1.58×104 W/m21.58 \times 10^4 \mathrm {~W} / \mathrm { m } ^ { 2 }1.58×104 W/m2

Light from a Laser Forms a 1 $1.58 \times 10^4 \mathrm {~W} / \mathrm { m } ^ { 2 }$